The weather on the flight across Germany had been cloudy. But when the first wave of Lancasters arrived over Dresden, there was a gap in the cloud cover. There were no fighters to oppose them and no flak. The aiming-point was over the north end of the Altstadt, the old city.

Each bomber fanned out on a slightly different heading, so that the target was completely covered. The first bombs fell at 10.13pm on that Shrove Tuesday night. The last fell at 10.28. In those 15 minutes, just over 880 tons of high explosive, parachute mines and incendiaries went down. 'Good work, that's nice bombing,' said the master bomber over his radio.

The second wave, delayed in order to catch the firefighters and rescue teams out in the streets, came in at 1.21 in the morning. The fires in the Altstadt were so huge, visible to the aircrews 50 miles off, that the raid leaders decided to move their target to inner districts of Dresden beyond the fires. In 24 minutes, about 1,755 tons of bombs were dropped. Next day, the US Eighth Army Air Force delivered a massive but ragged raid through cloud (three Flying Fortress groups got lost and bombed Prague by mistake).

What happened down below is an indelible part of German, British and world memory. The firestorm howled through blazing streets, carrying along trees and human beings as the asphalt boiled. Hundreds who took refuge in outdoor water tanks drowned, suffocated or were cooked alive. Untold thousands died in shelter cellars as the firestorm tore away the oxygen at ground level and filled their lungs with searing carbon monoxide.

The most beautiful baroque city in Europe became ashes and rubble. Dresden became and remains a symbol of war's horror, and for the war's victors, the source of an unbearable question: why did we do this? Did Dresden bring the Allies down to the level of those who razed Warsaw and drove the Jews into the gas chambers?

As Frederick Taylor says, a whole generation has taken its notion of the tragedy from David Irving's 1963 book The Destruction of Dresden. Irving's aim was to prove that Dresden was a deliberate war crime which debased the Allies to moral equivalence with the Nazis. Taylor's carefully researched book, based on documents and interviews, tries to provide a more accurate account of why the Dresden raid happened and what really took place that night. He does not excuse, but he disposes of some enduring myths.

Was Dresden an 'innocent' city, without war industries or military importance? It was not. The city's peacetime luxury industries had been converted to high-technology war production, especially in optics and electronics. The railway directorate in Dresden controlled traffic throughout south-eastern Germany and Bohemia, and an average of 28 troop or military trains passed through the main station daily.

Was the attack a deliberately planned act of terror against civilians? Yes, but not only that and not to be judged out of its context. The Dresden raid was only one in a programme of huge attacks on the centres of German cities at this stage in the war, designed to terrorise by firestorms but also to sever communications bringing reinforcements to the Eastern Front.

It was singularly destructive only because it happened to meet 'perfect' conditions: the cloud gap, the lack of defences, an inflammable town-heart, a failure to build public bunkers, a population which made the fatal mistake of staying below ground instead of emerging and trying to fight the fires left by the first wave.

On the other hand, Air Marshal Arthur Harris had made civilian morale the 'primary objective' as long ago as 1942, through the 'Area Bombing Directive'. Hamburg had been obliterated by firestorm, killing perhaps 40,000 people, in July 1943. A year later, Air Marshal Portal had recommended concentrating Bomber Command's strength into a single, huge blow against one hitherto undamaged city. And at the Yalta conference in early February 1945, the Russians seem to have suggested a major raid on Dresden to some members of the British delegation.

How many died? Irving produced a contemporary document reporting 202,400 registered dead and predicting that another 250,000 would be found. Taylor shows that Irving's copy had been faked by the Nazis, who had simply added a nought to each total. His own estimate is between 25,000 and 40,000, almost all civilians and refugees. Fearful as this is, Taylor reminds us that some places suffered proportionately worse. The RAF hit undefended Pforzheim 10 days later, a much smaller city, and killed 17,600 people, a quarter of the entire population. Dresden lost 'only' 5 per cent.

Taylor disproves another myth, still widely believed, that the American raiders next morning used fighters to strafe survivors fleeing the city or huddling on the Elbe river meadows. This did not happen. And he tackles the modern assumption that the whole area-bombing campaign was a murderous mistake which did not even cripple German war production. Taylor argues, fairly convincingly, that the high-technology losses and the diversion of manpower caused by bombing were becoming unsustainable by early 1945.

Was the annihilation of Dresden necessary? No, but it was probably inevitable. The shrewdest verdict comes from the late novelist WG Sebald, who said that by 1945 the impetus of the colossal investment of men, material and planning in the bombing offensive had become unstoppable. To let the aircraft and their freight stand idle on the East Anglian runways, he wrote ironically, 'ran counter to any healthy economic instinct'.

This might have been one of those pert, self-important histories which boast that they are debunking all previous judgments. It is anything but that. As Taylor dismantles more myths, he becomes increasingly appalled by the truth which remains. This is a rigorous book, written by a man who does not deny his own feelings.

A couple of years ago, on the night of 13 February, Taylor followed the Dresdeners as they laid wreaths at the cemetery, lit candles around the ruins of the Frauenkirche and sang songs on the Altmarkt where 7,000 bodies were incinerated. Then he walked alone down to the banks of the dark Elbe.

Suddenly, the church bells begin to peal, 'marking the day and the hour when Bomber Command's fleet swept down towards its helpless target. And as it first learned to do on this night almost 60 years ago, a whole city holds its breath'.